检查类型是否通用

Question

我正在尝试实现一个代码分析器,它将另一个Java文件作为输入.对于每个变量声明,我想检查变量所属的类型是否是通用的.有一个简单的方法吗？

例如,我想它:

isGenericType("HashSet") -> true
isGenericType("int") -> false

我可以创建一个包含所有泛型类型的注册表,但问题是如果我实现自定义泛型类型,那么我每次都必须更新注册表.有一些简单的解决方案吗？

Answer 1

即使HashSet可以是通用的,类型HashSet本身(没有<T>)也是原始类型.因此,我会采用扫描声明变量的实际类型的方法,可能在类型上应用正则表达式以查看尖括号是否存在:

isGenericType --> matches the pattern [a-zA-Z_\$][\w\$]*<[a-zA-Z_\$][\w\$]*>

如果要严格考虑有效标识,可以在Java语言规范中检查其定义:

标识符:

IdentifierChars但不是Keyword或BooleanLiteral或NullLiteral

IdentifierChars:

JavaLetter {JavaLetterOrDigit}

JavaLetter:

任何Unicode字符都是"Java字母"

JavaLetterOrDigit:

任何Unicode字符,即"Java字母或数字"

"Java letter"是该方法Character.isJavaIdentifierStart(int)返回true 的字符.

"Java letter-or-digit"是该方法Character.isJavaIdentifierPart(int)返回true 的字符.

Answer 2

我认为这与您所寻找的类似:

它打印true为java.util.HashSet.

但false对java.lang.Object.

public class TestGenerics
{
    public static boolean isGenericType(String s) throws ClassNotFoundException
    {
        Class c = Class.forName(s);
        return c.getTypeParameters().length > 0;
    }

    public static void main(String[] args) throws ClassNotFoundException 
    {
        System.out.println(isGenericType("java.util.HashSet"));
        System.out.println(isGenericType("java.lang.Object"));
    }
}

Answer 3

这将通过对象,类或类名进行测试.

更新:基于有用的评论对此代码的几个修订提供了一些有趣的测试用例.但是,最终问题的适当解决方案恰恰取决于问题的定义方式.请参阅早期版本和评论.

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.HashMap;

public class GenericTest
{
    public static void main(String[] args)
    {
        try
        {
            new GenericTest().testAll();
        } catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }

        System.exit(0);
    }

    public void testAll() throws ClassNotFoundException, InstantiationException, IllegalAccessException
    {
        Object a = new HashMap<String, Object>();
        Object b = new HashMap();
        int c = 0;

        isGeneric(a);
        System.out.println("\n");
        isGeneric(b);
        System.out.println("\n");
        isGeneric(c);
        System.out.println("\n");
        isGeneric("java.util.HashMap");
        System.out.println("\n");
        isGeneric("java.lang.Integer");
        System.out.println("\n");

        isGeneric(new TestA());
        System.out.println("\n");
        isGeneric(new TestB());
        System.out.println("\n");
        isGeneric(new TestB<String>());
        System.out.println("\n");
        isGeneric(new TestC());
        System.out.println("\n");
        isGeneric(new TestD());
        System.out.println("\n");
        isGeneric(new TestE());
        System.out.println("\n");

        return;
    }

    public static void isGeneric(String className) throws ClassNotFoundException, InstantiationException, IllegalAccessException
    {
        GenericTest.isGeneric(Class.forName(className));
        return;
    }

    public static boolean isGeneric(Object o)
    {
        return isGeneric(o.getClass());
    }

    public static boolean isGeneric(Class<?> c)
    {
        boolean hasTypeParameters = hasTypeParameters(c);
        boolean hasGenericSuperclass = hasGenericSuperclass(c);
//      boolean hasGenericSuperinterface = hasGenericSuperinterface(c);
//      boolean isGeneric = hasTypeParameters || hasGenericSuperclass || hasGenericSuperinterface;
        boolean isGeneric = hasTypeParameters || hasGenericSuperclass;

        System.out.println(c.getName() + " isGeneric: " + isGeneric);

        return isGeneric;
    }

    public static boolean hasTypeParameters(Class<?> c)
    {
        boolean flag = c.getTypeParameters().length > 0;
        System.out.println(c.getName() + " hasTypeParameters: " + c.getTypeParameters().length);
        return flag;
    }

    public static boolean hasGenericSuperclass(Class<?> c)
    {
        Class<?> testClass = c;

        while (testClass != null)
        {
            Type t = testClass.getGenericSuperclass();

            if (t instanceof ParameterizedType)
            {
                System.out.println(c.getName() + " hasGenericSuperclass: " + t.getClass().getName());
                return true;
            }

            testClass = testClass.getSuperclass();
        }

        return false;
    }

    public static boolean hasGenericSuperinterface(Class<?> c)
    {
        for (Type t : c.getGenericInterfaces())
        {
            if (t instanceof ParameterizedType)
            {
                System.out.println(c.getName() + " hasGenericSuperinterface: " + t.getClass().getName());
                return true;
            }
        }

        return false;
    }

    public interface TestX<X> { }

    public interface TestY extends TestX<String> { }

    public class TestA implements TestY { }

    public class TestB<V> extends TestA { }

    public class TestC extends TestB<String> { }

    public class TestD extends TestA { }

    public class TestE extends TestC { }
}

运行上面代码的结果:

java.util.HashMap hasTypeParameters: 2
java.util.HashMap hasGenericSuperclass: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl
java.util.HashMap isGeneric: true


java.util.HashMap hasTypeParameters: 2
java.util.HashMap hasGenericSuperclass: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl
java.util.HashMap isGeneric: true


java.lang.Integer hasTypeParameters: 0
java.lang.Integer isGeneric: false


java.util.HashMap hasTypeParameters: 2
java.util.HashMap hasGenericSuperclass: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl
java.util.HashMap isGeneric: true


java.lang.Integer hasTypeParameters: 0
java.lang.Integer isGeneric: false


GenericTest$TestA hasTypeParameters: 0
GenericTest$TestA isGeneric: false


GenericTest$TestB hasTypeParameters: 1
GenericTest$TestB isGeneric: true


GenericTest$TestB hasTypeParameters: 1
GenericTest$TestB isGeneric: true


GenericTest$TestC hasTypeParameters: 0
GenericTest$TestC hasGenericSuperclass: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl
GenericTest$TestC isGeneric: true


GenericTest$TestD hasTypeParameters: 0
GenericTest$TestD isGeneric: false


GenericTest$TestE hasTypeParameters: 0
GenericTest$TestE hasGenericSuperclass: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl
GenericTest$TestE isGeneric: true